To remove brown skin, bring a pot of water to a boil. Add pistachios and remove from heat. Soak for 30 seconds or so and transfer into a bowl of ice water.
Drain the pistachios onto a clean kitchen towel. Rub it gently and peel off the brown skin.
In a food processor, put cleaned pistachios and process for 5-10 minutes, until pastey. It'll go through a few stages; be patient.
Add oil to help the paste to blend more easily, and continue to process for another 5-10 minutes, or until it is nice and smooth.
Store in an airtight container in the fridge for up to 1 weeks, or freeze for up to 3 months.
